This invention relates to a magnetic sensor utilized in brushless direct current motors and in magnet position detecting devices.
In accordance with miniaturization and actuation at low voltage of brushless direct current motors and of position detecting devices, the demand for a highly sensitive magnetic sensor has been raised.
In the early period, a highly sensitive magnetic sensor employing Hall devices was made of semiconductor materials such as GaAs, InSb or the like, which have high mobility characteristic.
However, in manufacturing a one chip magnetic sensor by utilizing the above materials, it is difficult to integrate comparators and other logic circuits in addition to the Hall devices onto the one chip.
In recent years, a Hall device magnet sensor employing a silicon single crystal as a semiconductor material has been developed because this type makes it easy to integrate one chip. Especially, a P-silicon single crystal substrate having the crystal surface (100) has been preferably used as a standard material since it is easy to be processed.
However, the above mentioned Hall device formed on a silicon single crystal still has the following problem:
The silicon single crystal has large piezo-resistance effect and also anisotropy. Piezo-resistance effect is the phenomenon that resistance is generated in a device formed on a chip by adding stress to the semiconductor chip. The piezo-resistance effect causes to generate offset voltage at the output terminals of the Hall devices on the silicon chip. The offset voltage is generated at the output terminals even though magnetic fields are not applied to the sensor. A silicon chip Hall device has the high offset voltage, so that errors in detection are brought about. Chip mounting (diebonding, molding) is thought to be a source of the stress from the outside. Provided that the magnetic sensitivity of a Hall device is 20 mV/KGanss, the error of 50 Ganss in detection is brought about when 1 mV offset voltage is generated by the piezo-resistance effect. Usually, not less than 100 Ganss variation have been unfavorably produced at -30.degree. C..about.100.degree. C.